In the existing semiconductor processing, plasma processing apparatuses are widely used to process semiconductor wafers, so as to obtain micro dimension semiconductor devices and conductive connections. The plasma apparatus usually includes Capacitively Coupled Plasma (CCP) reaction chamber or Inductively Coupled Plasma (ICP) reaction chamber. These apparatuses usually have two RF power supplies, one is used to ionize the reaction gas inputted into the reaction chamber to generate plasma, and the other one is used to control the ion energy incident to the surface of the wafer.
The plasma processing device as shown in FIG. 1 includes a reaction chamber 100. A base 22 is contained by the reaction chamber, and a lower electrode is included in the base 22. A fixing device for fixing the substrate to be processed, such as an electrostatic chuck 21, is provided above the lower electrode, and a wafer 20 is fixed on the upper surface of the electrostatic chuck 21. An edge ring 10 surrounding the electrostatic chuck and the wafer is also provided. In the reaction chamber 100, a gas showerhead 11 is provided right above the base, and the gas showerhead is connected to a gas source 110, for supplying gas to the reaction chamber uniformly. Capacitive coupling is formed by the gas showerhead functioning as an upper electrode and the lower electrode in the base. A first RF power supply 31 is electrically connected to the lower electrode via a match 1, a second RF power supply 32 is electrically connected to the lower electrode via a match 2, and both of the first RF power supply and the second RF power supply have a fixed RF frequency. Since the impedance of the plasma will change when parameters such as gas pressure of the plasma, RF power and plasma concentration change, the parameter of the input power and the impedance need to be adjusted continuously to minimize the reflected power. In the plasma processing, both the first RF power supply 31 and the second RF power supply 32 supply powers to the lower electrode, and the match 1 and the match 2 can adjust the impedance via interior adjustable components respectively to minimize the RF reflected power. The frequency of the RF power source 31 or 32 may also be adjusted to much quickly adjust the input impedance. However, both the adjusting of the impedances of the matches 1, 2 and the adjusting of the frequencies of the RF power sources 31, 32 described above are achieved by moving an mechanical component (such as a variable capacitor or a variable inductor driven by a machine). In addition, in the procedure for minimizing the reflected power, the mechanical component described above moves in any direction, then the mechanical component is controlled to move to an appropriate position according to the feedback value of the reflected power, and therefore the procedure for sweeping the impedance of the match or the frequency of the RF power supply takes a long time, which reaches a second level, such as a time greater than 1 second.
Presently, a pulse plasma processing technology is required in many plasma processing. In some time periods of the processing, the RF power supply does not continuously supply powers, the output power will alternatively change between an on state and an off state or a high power state and a low power state; the waveform of the output power is in a pulse form, so it is referred to pulse plasma processing. The alternate frequencies are generally about 10K-100 KHZ, and the duty cycle of the on-off state may be adjusted in a range of 10%-90% according to requirements. In this way, each switching between the on state and the off state or between the high power state and the lower power state will cause fast change of the impedance in the reaction chamber, and the time of each change is in a millisecond level or even in a microsecond level. In the traditional art, auto frequency tuning (AFT) in the match circuit or the RF power supply is employed, and since the response time is much longer than millisecond level, the requirement of the pulse plasma processing can not be met.
Therefore, in view of the above reasons, there is a need for a fast impedance matching method in the pulse plasma processing by using only the existing hardware or by simply adjusting the existing hardware conditions.